1. Field of the Invention
This invention relates to an optical system for reading the altitude angle scale and the horizontal angle scale of a theodolite in the same view field.
2. Description of the Prior Art
As the optical system of the device of this type, there has been a construction as shown in FIG. 1 of the accompanying drawings wherein an altitude angle scale 1a (hereinafter referred to as the V scale) formed on an altitude angle scale plate 1 is imaged on the same plane as a horizontal angle scale 2a (hereinafter referred to as the H scale) formed on a horizontal angle scale plate 2 by a relay lens 3, and is further imaged on a focusing screen 5 by an objective lens 4 through prisms 13 and 14, and further the reading of the V scale and the H scale is effected by an eye-piece 6 through a prism 15. There has also been a construction as shown in FIG. 2 of the accompanying drawings wherein the V scale 1a on an altitude angle scale plate 1 and the H scale 2a on a horizontal angle scale plate 2 are imaged on a focusing screen 5 by two objective lenses 4 and 4' provided on different light paths and the V and H scales are read through an eye-piece 6. In either of these constructions, two imaging systems such as a relay lens and an objective lens have been requisite and this has meant a great number of lenses required and accordingly a complicated construction and also, the adjustment of the same focus and the adjustment for obtaining a predetermined magnification have been difficult and required a long time. Particularly, in the former construction (FIG. 1), the H scale is imaged once, whereas the V scale is imaged twice and this has led to a disadvantage that there occurs a difference between the resolving powers of the two scales.